Data hiding has become an intensive research area in recent years. Most multimedia data hiding techniques modify and therefore distort the cover media during the data hiding process. Even though the distortion is often small and imperceptible to human visual systems (HVS), the original cover media usually cannot be restored completely. In other words, most of these data hiding techniques are nonreversible, which is not acceptable for some sensitive applications, such as legal and medical imaging.
For legal, medical, and other sensitive applications, reversible data hiding is desired in order to extract the embedded data as well as to recover the original host signal. Reversible (also often referred to as invertible, lossless, or distortion-free) data hiding has been a very active research subject in the last few years. Many reversible data hiding schemes have been reported, such as in documents numbered 1-11 below.
In documents [2] and [8], identified below, modulo-256 addition is utilized to avoid overflow and underflow and thus achieves reversibility. The scheme proposed by Fridrich et al. [3] losslessly compresses the bit-planes in the spatial domain and hence saves space to embed the payload (to-be-embedded data) and overhead (bookkeeping data) to achieve reversible data hiding. The payload of this technique is quite small owing to the rather limited compression ratio that can be achieved in the spatial domain. Based on this, a general least significant bit-plane (GLSB) embedding technique in the spatial domain was proposed by Celik et al. [6]. The payload and imperceptibility of embedded data are largely improved because of the more efficient compression technique used therein. Domingo-Ferrer et al. [5] proposed a spatial-domain spread-spectrum data hiding method. However, it is only reversible with respect to the modified version of the original host signal. Xuan et al. [7] proposed a reversible data hiding algorithm carried out in the integer wavelet transform (IWT) domain.
Tian [10] embeds the data using a difference expansion technique, resulting in an improved reversible data hiding method in terms of data embedding capacity versus visual quality of marked images. Yang et al. [11] proposed a reversible data hiding technique using the companding technique. This technique embeds data in discrete cosine transform (DCT) coefficients.